continental drift and plate tectonics drift and plates continental drift concept introduction did...
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CONTINENTAL DRIFT AND
PLATE TECTONICS
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DRIFT AND PLATES• Continental drift concept
• Introduction
• did continents originate at their present locations or did they move to where they are today?
• drift concept supplied information to aid in the formulation of rock plate or tectonic plate concept
• a solid lithosphere floating on top of the asthenosphere gives an idea of how plates can float
• Accretion of continental material took place
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DRIFT AND PLATES• convection cells in Earth’s interior is the
force which split the lithosphere and are the driving force in continental separation
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DRIFT AND PLATES Accretion of Continental Materials during Drift---Western USA
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DRIFT AND PLATES• who was the first to observe this map fit? • Alfred Wegener was the first to publish a
summary of ideas about continental drift in 1912.
• some ideas in the publication were: 1) the protocontinent or supercontinent was named Pangaea; 2) southern section was named Gondwana or Gondwanaland and northern section, Laurasia; 3) the protocontinent broke in pieces about 150-200 million years ago
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DRIFT AND PLATES• Some important data confirming continental
drift
• map fit--already mentioned
• mountain chains formed on continents with longitudinal axes perpendicular to movement of the continents--examples: Himalayan, Rocky Mountain and Andes Mountain chains
• same fossils (in rocks),same rocks , mountain ranges, and glacial features located on different continents in areas representing prejoined positions prior to continental drift
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DRIFT AND PLATES• Initial ideas of continental drift
• jig saw puzzle or map fit of continents
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Matching of Fossils from Common Locations on Separated Continents
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Matching of Mountain Chains from Common Locations on Separated Continents
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Matching of Glacial Deposits from Common Locations on Separated Continents
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DRIFT AND PLATES• presence and shape of global ocean ridge
• a ridge is a raised region on ocean basin which is believed to represent prejoined or splitting area of separated continents--the shape of the ridge contours shape of coast lines of separated continents--- this is most evident in the mid Atlantic ocean
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Global Ocean Ridge
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DRIFT AND PLATES• seafloor spreading
• age of rocks located on equivalent positions on both sides of the ridge are the same--rocks progressively increase in age away from the ridge
• magnetic intensities in the rocks are found to be the same on equivalent sides of the ridge--on both sides of ridge magnetic intensity alternates between normal(high intensity) and abnormal(low intensity)
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DRIFT AND PLATES
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Magnetic Intensities and Sea Floor Spreading
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DRIFT AND PLATES• Lithospheric plates and plate tectonics
• where are the spreading continents going?
• the answer was important in initiating the rock plate concept
• rock sections or plates which diverge from spreading zones move towards or converge on subduction zones
• Rock plates
• ocean basin and continental sections float in the asthenosphere, some plates diverge, some converge and some move parallel (to each other)
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DRIFT AND PLATES• Classification of rock plate boundaries
• volcanism and seismic activity are abundantly associated with plate boundaries
• boundaries are classified as divergent, convergent, or transformed boundaries
• divergent boundary--includes all ridges and rifts--tensional forces caused by convection cells drive the plates apart
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DIVERGENT PLATE BOUNDARY
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DRIFT AND PLATES• kinds of divergent plate boundaries--1)ocean
basin to ocean basin boundary;
example is the mid ocean ridge
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DRIFT AND PLATES• 2) continental to continental boundary
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DRIFT AND PLATES• convergent boundaries--includes all
subduction boundaries--compressional forces caused by convection cells drive plates towards each other--volcanic arcs are associated with convergent boundaries
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Convergent Plate boundary
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3 types of convergent plate boundaries
1) Ocean basin to continental boundary
(Example is the Cascade Mountain chain)
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2) Ocean basin to ocean basin boundary
(Examples are Aleutian Islands and Japan)
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Aleutian Islands and Japan
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3) Continental to continental plate boundary
(Example is India and Asian continent boundary)
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DRIFT AND PLATES• transformed boundary--plates move
parallel to boundary
Example are those off the Coast of Western U.S.A.
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DRIFT AND PLATES• Major Plates on Earth and Movement Rates
Movement rates are about as fast as your fingernails grow